This invention is concerned with a process and device for evporating large amounts of low boiling gases, especially for the evaporation of nitrogen for fighting mine fires. The invention is, however, not restricted to this use, but can be adapted to all cases where large amounts of gas must be obtained by evaporation of the liquid phase of the gas. This can, for example be the preparation of inert gas to render tankers inert, or the evporation of liquefied natural gas for peak load service.
Mine fires used to be combatted by walling off all accesses to the furnace of the fire in order to choke off the supply of air to the location of the fire. It would usually take years until such a fire would choke by itself on account of scarce air supply. It happened often, thereby, that the fire would flare up anew as soon as sealing walls were opened.
With mine fires, the requirements are set. Since nowadays very expensive machines are put in, it represents a very high financial loss, if these machines cannot, under the circumstances be used for years. Under these circumstances, they even represent a total loss, if they are technologically revised during the years of the fire. Therefore, it is desirable to more quickly bring mine fires under control and to extinguish them faster.
Successful in this area has been gaseous nitrogen, which is carried by a pipeline through the shaft and brought directly to the furnace of the fire by means of tubular probes, so that the fire is choked. As a rule, one usually succeeds, in this manner to extinguish the fire within fewer weeks or months.
In connection with this, very large quantities of nitrogen in the magnitude of several thousand Nm.sup.3 /hr. required. As a rule, this nitrogen cannot be obtained in the gaseous state from an air separation plant, so that it must be channeled into the shaft in liquid form and evaporated there. For this, one often uses a heat exchanger unit with water as the exchange medium. The water is heated in a separate chamber by immersion heaters and rotated by a pump. The liquid nitrogen flows through tubular coils on the rotating water bath and evaporates. Such an installation is extensive and requires a high investment cost. Considerable transportation and installation costs arise from the weight of the equipment. The bottom must be provided with a stable foundation. Also the operation of the equipment is expensive and complicated. The operation of the blowers or compressors for the immersion heaters and for the water circulating pump causes a substantial current demand. Adjustment is difficult since the temperature of the evaporated nitrogen as well as that of the circulating water must be tuned to each other.